Fuel cells consuming a fuel gas (hereafter also referred to as anode gas), such as hydrogen, and oxygen to generate electric power have lately been noted as the novel energy source. In a fuel cell system equipped with such fuel cells, regulators (pressure regulators) are used to lower the pressure of an anode gas supply from a high-pressure anode gas supplier (for example, a hydrogen tank) to an adequate pressure level and then introduce the pressure-regulated anode gas to the fuel cells. The gas supplier is equipped with a shutoff valve (supplier shutoff valve) to allow and stop the supply of the anode gas. The anode gas is flowed from the gas supplier to the fuel cells through a flow path called an anode gas supply conduit. The gas supplier and the fuel cells are respectively located on an upstream side and on a downstream side of the anode gas supply conduit. Among the regulators located in the downstream of the supplier shutoff valve, a most upstream regulator is called a high pressure regulator.
For the safety measure, gas leakage detection is conventionally performed to check any leakage of the anode gas from the supplier shutoff valve. A typical procedure of the gas leakage detection reduces the pressure in a preset flow path section of the anode gas supply conduit (hereafter referred to as the leakage detection flow path) located in the downstream of the supplier shutoff valve and the high pressure regulator and detects a leakage of the anode gas from the supplier shutoff valve with a pressure sensor provided in the downstream of the high pressure regulator in the leakage detection flow path. The pressure reduction is required to lower the pressure in the upstream of the high pressure regulator to a level substantially equivalent to the pressure in the downstream of the high pressure regulator in the leakage detection flow path. The gas leakage detection is performed not with a pressure sensor provided in the upstream of the high pressure regulator but with a pressure sensor provided in the downstream of the high pressure regulator. This is because the pressure sensor located in the upstream of the high pressure regulator is required to have high pressure resistance and accordingly has relatively low pressure measurement accuracy.
A typical procedure of the pressure reduction for the gas leakage detection causes power generation of the fuel cells to consume the anode gas, after closure of the supplier shutoff valve as disclosed in Japanese Patent Laid-Open No. 2003-308868.
A relatively large amount of the anode gas is the target of pressure reduction of lowering the pressure in the upstream of the high pressure regulator to the level substantially equivalent to the pressure in the downstream of the high pressure regulator in the leakage detection flow path. The conventional method of consuming the anode gas by the simple power generation of the fuel cells as in the cited document, however, takes a relatively long time. One possible measure against this drawback causes power generation of the fuel cells under a high pressure to quickly consume the anode gas in the leakage detection flow path and attain high-speed pressure reduction. This, however, causes supply of large electric power to a secondary battery or another destination of consuming the generated electric power and leads to another drawback of poor durability of the secondary battery or another destination.